Consistent use of strings in provision.sh

Use echo in favor of printf to not have to add \n each time; use quotation marks around strings consistently; minor string changes
Use `-e` flag to enable interpretation of backslash escapes

We do use `\n` from time to time for additional spacing around lines. `echo` does not handle this by default until a flag is used to do so.

Work towards #133
Small formatting change in terminal output

Work toward #133
Updated contributors list
README tweaks
Refresh, update, and document Nginx configuration

Thanks to some excellent reading provided by H5BP in their [nginx server configs repo](https://github.com/h5bp/server-configs-nginx/blob/master/nginx.conf), I was able to clarify and better document a few of the settings in our Nginx configuration as well as add a couple other directives.

Things seem to be working fine currently, please open up an issue if you start noticing weird Nginx behavior
Merge branch 'master' of https://github.com/10up/varying-vagrant-vagrants